Heat-exchanger

ABSTRACT

A heat-exchanger, especially for vehicle gas turbines which comprises tubes arranged between chambers, through which flows a first medium, and a housing surrounding the tubes, through which flows a second medum; the thermally strongly stressed wall portions of the chambers are provided with expansion folds within the area of the terminations of the tubes in the chambers.

United States Patent 1191 Tank et al. p

1451 June 28, 1974 1 HEAT-EXCHANGER [73] Assignec: Daimler-Benz Aktiengesellschaft,

Stuttgart, Germany 221 Filed: July 28,1972

121 Appl. No.: 276.173

130] Foreign Application Priority Data July 30, 1971 Germany 2138109 [52] US. Cl. 165/83 [51] Int. Cl F28f 7/00 [58] Field of Search 165/81-83, 165/96, 145, 130, 143

[56] References Cited UNITED STATES PATENTS 1,993,539 3/1935 Anthony et a1, 165/81 UX -20 1 e1 1 w :42 l

FOREIGN PATENTS OR APPLICATIONS 763,896 12/1956 GreatBritain 165/83 781,571 2/1935 France 165/83 Primary ExaminerCharles J. Myhre Assistant Examiner-Theophil W. Streule, Jr. Attorney, Agent, or FirmCraig and Antonelli [57] ABSTRACT A heat-exchanger, especially for vehicle gas turbines which comprises tubes arranged between chambers,

through which flows a first medium, and a housing surrounding the tubes, through which flows at second medum; the thermally strongly stressed wall portions of the chambers are provided with expansion folds within the area of the terminations of the tubes in the chambers.

25 Claims, 12 Drawing Figures PATENTEUJum I974 SHEET 2 0F 4 FIG. 6

HEAT-EXCHANGER The present invention relates to a heat-exchanger, especially for vehicle gas turbines, which is assembled from tubes or pipes arranged between chambers within which flows a first medium, and from a housing enclosing the pipes, through which flows a second medium.

Such types of heat-exchangers are thermally highly stressed by high temperatures, by the considerable temperature drop of the individual media between inlet and outlet as well as above all by the large temperature differences between the two media, for example, between the strongly heated exhaust gases and the relatively cold suction air. On these high thermal stresses caused thereby in the structural parts of the heatexchanger may be superimposed additional stresses conditioned by rapid temperature fluctuations, for example, during load changes of a gas turbine. The fastening places of the tubes which are thermally loaded particularly highly, at their termination in the chambers are, for the most part, exposed additionally to considerable mechanical loads and stresses due to bending moments and tensional forces which are caused by the excess pressure of a medium. In particular, the heatexchangers of portable or locomotive gas turbines are endangered thereby which requires smaller dimensions and a slight weight, and which for that reason possess only slight wall thicknesses.

The present invention is concerned with the task to eliminate the danger of damages due to high thermal stresses and to provide a heat-exchanger that is able to withstand also high loads and stresses. This is achieved according to the present invention in that thermally strongly stressed wall parts of the chambers within the area of the terminations of the tubes or pipes are provided with expansion folds. The expansion folds equalize differently large thermal expansions due to their ready deformability so' that dangerous stresses which otherwise occur in particular at the connecting places of the pipes, cannot form.

According to a further feature of the present invention, individual expanding folds are inserted into cutouts in the chamber wall and are connected therewith, for example, by welding. The expansion folds can thus be arranged in a simple manner at all those places, where the largest thermal expansions occur. Such expansion folds can also be installed subsequently into the chambers of an existing heat-exchanger.

Accordingly, it is an object of the present invention to provide a heat-exchanger which avoids by simple means the aforementioned shortcomings and drawpermits the installation of expansion folds in a simple manner at all those places where maximum thermal stresses occur.

Another object of the present invention resides in expansion folds for heat-exchangers which can be installed also subsequently in the chamber walls of existing heat-exchangers.

These and further objects, features and advantages of the present invention will become more apparent from the following description when taken in connection with the accompanying drawing which shows, for purposes of illustration only, several embodiments in accordance with the present invention, and wherein:

FIG. 1 is a schematic cross-sectional view through a single-pass cross-current heat-exchanger in accordance with the present invention, taken along line II of FIG.

FIG. 2 is a schematic cross-sectional view through the heat-exchanger of FIG. 1, without housing thereof, and taken along line II-II of FIG. 1;

FIG. 3 is a schematic cross-sectional view through a double-cross-current heat-exchanger in accordance with the present invention, taken along line III-III of FIG. 4;

FIG. 4 is an elevational view of the heat-exchanger of FIG. 3 with the housing thereof removed;

FIG. 5 is a partial cross-sectional view illustrating, on an enlarged scale, the expansion fold shown in FIG. 3;

FIG. 6 is a partial cross-sectional view taken along line VIVI of FIG. 5;

FIG. 7 is a cross-sectional view, on an enlarged scale, through an apertured plate of a further embodiment of the heat-exchanger in accordance with the present invention, taken along line VII-VII of FIG. 8;

FIG. 8 is a cross-sectional view through the apertured plate of FIG. 7, taken along line VIII-VIII of FIG. 7;

FIG. 9 is a plan view on the apertured plate according to FIG. 7;

FIG. 10 is a schematic cross-sectional view through a ring-shaped heat-exchanger in accordance with the present invention taken along line X-X of FIG. 11;

FIG. 11 is a partial schematic cross-sectional view through the heat-exchanger of FIG. 10 taken along line XIXI of FIG. 10; and

FIG. 12 is a plan view, on an enlarged scale, on a part of the apertured plate according to FIG. 11.

Referring now to the drawing wherein like reference numerals are used throughout the various views to designate like parts, and more particularly to FIGS. 1 and 2, the single-cross-current heat-exchanger schematically illustrated in these two figures for a vehicle gas turbine essentially consists of a housing 11 through which are conducted the exhaust gases of the turbine, and of a tube or pipe bundle 12 through which flows the air and thereby absorbs heat from the exhaust gases. The hot exhaust gases enter the heat-exchanger through the inlet aperture 13 and leave the same through the outlet or discharge aperture 14 in the cooled-off condition. The air flows through an inlet pipe connection 15 into a chamber 16 and from there through the tubes or pipes 17 of the tube bundle 12 into the chamber 18 serving as discharge manifold or collecting space which they leave in the heated-up condition through an outlet pipe connection 19. The flow direction of the exhaust gases and of the air are indicated by arrows.

Wall portions 20 and 21 of the chambers 16 and 18 in which terminate the tubes 17 and in which the tubes 17 are secured, are provided with expansion folds 22 and 23, respectively, which extend in each case in the flow direction of the hot gases between two adjacent tube rows 24 and 25 of the tube bundle 12. The expansion folds 22 and 23 absorb deformations of the wall portions 20 and 21 which expand differently strongly under the influence of the hot exhaust gases and the cold air. As a result thereof, damages due to stress peaks in the thermally strongly stressed wall portions 20 and 21 within the area of the terminations of the pipes 17 are avoided.

The double-cross-current heat-exchanger illustrated schematically in FIGS. 3 and 4 essentially consists of a housing 26, in which are arranged tube bundles 27 and 28 that connect the chambers 29 and 30 with a chamber 31. Hot exhaust gases flow into the housing 26 through the inlet aperture 32, circumcirculate the tube bundles 27 and 28 and leave the housing 26 through the discharge aperture 33. Cold air flows through an inlet pipe connection 34 into the chamber 29 and continues to flow through the tube bundle 27, the chamber 31 and the tube bundle 28 into the chamber 30 which it leaves by way of the discharge pipe connection 35.

The exhaust gases during the flow through the housing 26, give off heat to the air flowing in the tube bundles 27 and 28 and heat up the same. The strongest temperature differences thereby result within the area of the termination of the pipes 36 of the first row of the tube bundle 27, on which impinge at first the hot exhaust gases, in the chamber 29 from which starts the cold air.

For purposes of equalization of the differing thermal expansions resulting therefrom, expansion folds 38 are arranged in the thermally strongly stressed wall portions 37 of the chamber 29 which can readily deform. The expansion folds 38 are, as can be readily seen from FIGS. and 6, welded-in into corresponding cut-outs 39 in the chamber wall 40 in such a manner that they project into the chamber 29. The hollow space 41 surrounded by the expansion fold 38 is covered off with respect to the interior space 42 of the housing 26 by a sheet metal plate 43 in order to avoid that hot gases flow continuously through the expansion fold 38 and locally change the temperature field in an undesirable manner. By reason of the fact that the sheet metal plate 43 is welded to the chamber wall 40 only with its one side 44, changes in shape of the expansion fold 38 are not impaired. However, identical or similar expansion folds may also be provided in the corresponding area of the chamber 31 either alone or in addition to the expansion folds 38. This is applicable in particular if the air flows, not as indicated by the arrows in FIGS. 3 and 4 but in a direction opposite thereto.

FIGS. 7 and 9 illustrate an apertured plate 45 of a heat-exchanger in which are secured the tubes 46. The tubes 46 start from a chamber 47 and extend through the housing 48 to a further chamber (not shown). At thermally strongly stressed places within the area of the terminations of the tubes 46 in the chamber 47 expansion folds 49 projecting into the housing 48 extend through the apertured plate 45 and through some of the kept narrow so that the flow in the tubes 46 is impaired only insignificantly.

The ring-shaped heat-exchanger illustrated in FIGS. 10 to 12 consists essentially of a cylindrical housing 52, at the inner circumference of which a tube bundle generally designated by reference numeral 53 is arranged ring-shaped between apertured plates 54 and 55. The hot gases which give off the heat reach the interior space 58 of the housing 52 through a central inlet aperture 56 provided in an end face 57 of the housing 52 and leave the same after the radial through-flow through the tube bundle 53 by way of a discharge aperture 59 provided in the casing 60 of the housing 52. The gas to be heated flows through an inlet pipe connection 61 into an annular chamber 62, and from there by way of the tubes 63 of the tube bundle 53 into a further annular chamber 64 which it leaves by way of the discharge pipe connection 65. In a similar manner as in the preceding embodiment, expansion folds 66 extend through the apertured plate 54 and a portion of the tubes 63 of the tube bundle 53 within the area of the termination thereof in the apertured plate 54. The expansion folds 66 are arranged radially and thus are disposed, similar as the expansion folds of the already described embodiments, in the flow direction of the hot gases. Each of the expansion folds 66 is connected with three pipes 63. Between two expansion folds 66 is disposed on radial row of tubes 63 each, which do not include any connection with expansion folds. Depending on the thermal conditions, different arrangements of radial expansion folds may be utilized which may thereby be connected also with fewer or more than three tubes. It is also possible to radially offset with respect to one another adjacent expansion folds. in case of need, all tubes within the area of an apertured plate may also be connected with each other by radial expansion folds.

As indicated by the preceding embodiments, according to the present invention, individual ones or several expansion folds of different shape and dimensions may be arranged, respectively, at the thermally strongly stressed wall portions of the chambers within the area of the terminations of the pipes. The cut-outs or openings for the insertion of the expansion folds may be fabricated, for example, by a conventional electro-erosive process. The expansion folds, in lieu of being welded, can also be connected with the chamber walls and the pipes by brazing or by any other known, suitable means.

While we have shown and described several embodiments in accordance with the present invention, it is understood that the same is not limited thereto but is susceptible of numerous changes and modifications as known to those skilled in the art, and we therefore do not wish to be limited to the details shown and described herein but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.

We claim:

1. An expansion fold structure for a heat-exchanger which includes tubes arranged between chamber means and a housing surrounding the tubes, a first medium being adapted to flow through the tubes and a second medium being adapted to flow through the housing, characterized by expansion fold means provided in thermally strongly stressed wall portions of the chamber means, said expansion fold means being connected to said wall portions within the area of a respective chamber means where the tube means terminate, and characterized in that an expansion fold means forms a substantially hollow space that is substantially closed off with respect to the interior space of the housing by a baffle plate secured at only one side thereof to the chamber wall.

2. An expansion fold structure for a heat-exchanger which includes tubes arranged between. chamber means and a housing surrounding the tubes, a first medium being adapted to flow through the tubes and a second medium being adapted to flow through the housing, characterized by expansion fold means provided in thermally strongly stressed wall portions of the chamber means, said expansion fold means being connected tosaid wall portions within the area of a respective chamber means where the tube means terminate, and characterized in that the expansionfold means extends across at least two tube means and into the interior space of the housing traversed by the tube means, the expansion fold means being of smaller width than the inner diameter of a tube means.

3.'An expansion fold structure according to claim 2, characterized in that the expansion fold means engages into corresponding slot means provided in the tube means and is connected therewith.

4. An expansion fold structure according to claim 2, characterized in that the expansion fold means are arranged radially in an apertured plate.

5. A heat-exchanger arrangement comprising:

chamber means bounded on at least one side by chamber wall means,

tube means having open end portions terminating in said chamber means, said chamber means and tube I means being in fluid communication with one another for accomodating flow therethrough of a first fluid medium,

housing means surrounding said tube means for accomodating flow of a second fluid medium through said housing means in contact with outer surfaces of said tube means to thereby facilitate a heat exchange between the first and second mediums,

expansion fold means interposed between said tube 7 means and por tions of said chamber wall means for permitting thermal expansion movements of the tube means and the chamber wall means with respect to one another, said expansion fold means including a folded part in the chamber wall means which protrudes'into said chamber,

and a covering plate extending across the space formed externally of said chamber means by said folded part so that continuous flow of said second medium into said space is prevented, said covering plate being fixedly connected to said chamber wall means at only one side of said space so as to accomodate relative movement of those portions of the chamber wall means at opposite sides of said space.

6. An arrangement according to claim 5, wherein said tube means is connected to and supported by said chamber wall means.

7. An arrangement according to claim 6, wherein said housing means surrounds said chamber means.

8. An arrangement according to claim 6, wherein said tube means includes a plurality of separate tubes which are spaced from one another along the length of said chamber means and which extend transversely to said chamber means, said separate tubes and said chamber means being arranged such that certain of said tubes experience a greater temperature differential with respect to the flow of first medium therethrough and flow of second medium therearound than do other of said separate tubes, and wherein said folded part is positioned adjacent the connection of said chamber wall means with the tube which experiences the greatest temperature differential.

9. An arrangement according to claim 8, wherein a plurality of said folded parts are provided with a corresponding plurality of similarly arranged covering plates, said folded parts being positioned adjacent only a portion of the tubes.

10. An arrangement according to claim 5, wherein said folded part is formed as a part inserted into said chamber wall means and connected thereto.

11. An arrangement according to claim 10, wherein said folded part is welded to said chamber wall means.

12. An arrangement according to claim 5, wherein said folded part is of U-shaped cross-section with the open side of the U facing outwardly from said chamber wall means towards the space in said housing which accomodates the second medium.

13. An arrangement according to claim 11, wherein said folded part is of U-shaped cross-section with the open side of the U facing outwardly from said chamber wall means towards the space in said housing which accomodates the second medium.

14. A heat-exchanger arrangement comprising:

chamber means bounded on at least one side by chamber wall means,

a plurality of spaced tube means having open end portions terminating in said chamber means, said tube means extending outwardly through said chamber wall means and being connected to and supported by said chamber wall means, said chamber means and tube means being in fluid communication with one another for accomodating flow therethrough of a first fluid medium,

housing means surrounding said tube means for accomodating flow of a second fluid medium through said housing means in contact with outer surfaces of said tube means to thereby facilitate a heat exchange between the first and second mediums,

a continuous slot extending through a portion of said chamber wall means and intersecting at least one of said tubes, said slot extending completely through external wall portions of each of said at least one of said tubes, said slot extending along the length of each of said at least one of said tubes from a position within said chamber means to a position spaced outwardly of said chamber wall means where said second medium contacts the outer surfaces of said tube means,

and a folded part inserted in said slot and connected to said chamber wall means and said external wall portions of each of said at least one of said tubes for accomodating thermal expansion movements of the portions of the chamber wall means and tube means at opposite sides of said slot with respect to one another.

15. An arrangement according to claim 14, wherein said folded part is of U-shaped cross-section with the open end of the U facing the inside of the chamber means and the legs of the U extending parallel to the tube means.

16. An arrangement according to claim 15, wherein said slot and folded part intersect a plurality of said tube means.

17. An arrangement according to claim 16, wherein said slot and folded part extend completely through one of said tube means in a transverse direction so as to bisect said tube means.

18. An arrangement according to claim 17, wherein the extreme opposite longitudinal ends of said folded part open into respective tube means positioned at opposite sides of the tube means which is bisected.

19. An arrangement according to claim 18, wherein said folded part is sealingly connected to said chamber wall means and each of the three tube means intersected thereby such that flow of the first medium between the three tube means by way of the folded part is permitted while the flow of the second medium into said three tube means is prevented.

20. An arrangement to claim 19, wherein the maximum dimension of the folded part in a direction transverse to said slot is substantially smaller than the inside diameter of each of said tube means such that said folded part minimally interferes with the flow of the first medium through said tube means.

21. An arrangement according to claim 14, wherein the maximum dimension of the folded part in a direction transverse to said slot is substantially smaller than the inside diameter of each of said tube means such that said folded part minimally interferes with the flow of the first medium through said tube means.

22. An arrangement according to claim 14, wherein a plurality of folded parts are provided, each of said folded parts being similar to the above-mentioned folded part and being similarly arranged with respective slots constructed similarly to the above-mentioned slot and spaced from the above-mentioned slot so as to intersect other of the tube means. said folded parts being positioned so that only a portion of the total number of tube means are intersected thereby.

23. An arrangement according to claim 15, wherein a plurality of folded parts are provided, each of said folded parts being similar to the above-mentioned folded part and being similarly arranged with respective slots constructed similarly to the above-mentioned slot and spaced from the above-mentioned slot so as to intersect other of the tube means, said folded parts being positioned so that only a portion of the total number of tube means are intersected thereby.

24. An arrangement according to claim 23, wherein each of said folded parts intersect a plurality of said tube means, and wherein lines interconnecting the tubes intersected by respective ones of said folded parts extend substantially parallel to one another.

25. An arrangement according to claim 23, wherein each of said folded parts intersects a plurality of said tube means, wherein said chamber wall means is an annular shaped plate extending around a central axis of the heat exchanger arrangement, and wherein lines interconnecting the tube means intersected by respective ones of said folded parts extend radially with respect to said central axis. 

1. An expansion fold structure for a heat-exchanger which includes tubes arranged between chamber means and a housing surrounding the tubes, a first medium being adapted to flow through the tubes and a second medium being adapted to flow through the housing, characterized by expansion fold means provided in thermally strongly stressed wall portions of the chamber means, said expansion fold means being connected to said wall portions within the area of a respective chamber means where the tube means terminate, and characterized in that an expansion fold means forms a substantially hollow space that is substantially closed off with respect to the interior space of the housing by a baffle plate secured at only one side thereof to the chamber wall.
 2. An expansion fold structure for a heat-exchanger which includes tubes arranged between chamber means and a housing surrounding the tubes, a first medium being adapted to flow through the tubes and a second medium being adapted to flow through the housing, characterized by expansion fold means provided in thermally strongly stressed wall portions of the chamber means, said expansion fold means being connected to said wall portions within the area of a respective chamber means where the tube means terminate, and characterized in that the expansion fold means extends across at least two tube means and into the interior space of the housing traversed by the tube means, the expansion fold means being of smaller width than the inner diameter of a tube means.
 3. An expansion fold structure according to claim 2, characterized in that the expansion fold means engages into corresponding slot means provided in the tube means and is connected therewith.
 4. An expansion fold structure according to claim 2, characterized in that the expansion fold means are arranged radially in an apertured plate.
 5. A heat-exchanger arrangement comprising: chamber means bounded on at least one side by chamber wall means, tube means having open end portions terminating in said chamber means, said chamber means and tube means being in fluid communication with one another for accomodating flow therethrough of a first fluid medium, housing means surrounding said tube means for accomodating flow of a second fluid medium through said housing means in contact with outer surfaces of said tube means to thereby facilitate a heat exchange between the first and second mediums, expansion fold means interposed between said tube means and portions of said chamber wall means for permitting thermal expansion movements of the tube means and the chamber wall means with respect to one another, said expansion fold means including a folded part in the chamber wall means which protrudes into said chamber, and a covering plate extending across the space formed externally of said chamber means by said folded part so that continuous flow of said second medium into said space is prevented, said covering plate being fixedly connected to said chamber wall means at only one side of said space so as to accomodate relative movement of those portions of the chamber wall means at opposite sides of said space.
 6. An arrangement according to claim 5, wherein said tube means is connected to and supported by said chamber wall means.
 7. An arrangement according to claim 6, wherein said housing means surrounds said chamber means.
 8. An arrangement according to claim 6, wherein said tube means includes a plurality of separate tubes which are spaced from one another along the length of said chamber means and which extend transversely to said chamber means, said separate tubes and said chamber means being arranged such that certain of said tubes experience a greater temperature differential with respect to the flow of first medium therethrough and flow of second medium therearound than do other of said separate tubes, and wherein said folded part is positioned adjacent the connection of said chamber wall means with the tube which experiences the greatest temperature differential.
 9. An arrangement according to claim 8, wherein a plurality of said folded parts are provided with a corresponding plurality of similarly arranged covering plates, said folded parts being positioned adjacent only a portion of the tubes.
 10. An arrangement according to claim 5, wherein said folded part is formed as a part inserted into said chamber wall means and connected thereto.
 11. An arrangement according to claim 10, wherein said folded part is welded to said chamber wall means.
 12. An arrangement according to claim 5, wherein said folded part is of U-shaped cross-section with the open side of the U facing outwardly from said chamber wall means towards the space in said housing which accomodates the second medium.
 13. An arrangement according to claim 11, wherein said folded part is of U-shaped cross-section with the open side of the U facing outwardly from said chamber wall means towards the space in said housing which accomodates the second medium.
 14. A heat-exchanger arrangement comprising: chamber means bounded on at least one side by chamber wall means, a plurality of spaced tube means having open end portions terminating in said chamber means, said tube means extending outwardly through said chamber wall means and being connected to and supported by said chamber wall means, said chamber means and tube means being in fluid communication with one another for accomodating flow therethrough of a first fluid medium, housing means surrounding said tube means for accomodating flow of a second fluid medium through said housing means in contact with outer surfaces of said tube means to thereby facilitate a heat exchange between the first and second mediums, a continuous slot extending through a portion of said chamber wall means and intersecting at least one of said tubes, said slot extending completely through external wall portions of each of said at least one of said tubes, said slot extending along the length of each of said at least one of said tubes from a position within said chamber means to a position spaced outwardly of said chamber wall means where said second medium contacts the outer surfAces of said tube means, and a folded part inserted in said slot and connected to said chamber wall means and said external wall portions of each of said at least one of said tubes for accomodating thermal expansion movements of the portions of the chamber wall means and tube means at opposite sides of said slot with respect to one another.
 15. An arrangement according to claim 14, wherein said folded part is of U-shaped cross-section with the open end of the U facing the inside of the chamber means and the legs of the U extending parallel to the tube means.
 16. An arrangement according to claim 15, wherein said slot and folded part intersect a plurality of said tube means.
 17. An arrangement according to claim 16, wherein said slot and folded part extend completely through one of said tube means in a transverse direction so as to bisect said tube means.
 18. An arrangement according to claim 17, wherein the extreme opposite longitudinal ends of said folded part open into respective tube means positioned at opposite sides of the tube means which is bisected.
 19. An arrangement according to claim 18, wherein said folded part is sealingly connected to said chamber wall means and each of the three tube means intersected thereby such that flow of the first medium between the three tube means by way of the folded part is permitted while the flow of the second medium into said three tube means is prevented.
 20. An arrangement to claim 19, wherein the maximum dimension of the folded part in a direction transverse to said slot is substantially smaller than the inside diameter of each of said tube means such that said folded part minimally interferes with the flow of the first medium through said tube means.
 21. An arrangement according to claim 14, wherein the maximum dimension of the folded part in a direction transverse to said slot is substantially smaller than the inside diameter of each of said tube means such that said folded part minimally interferes with the flow of the first medium through said tube means.
 22. An arrangement according to claim 14, wherein a plurality of folded parts are provided, each of said folded parts being similar to the above-mentioned folded part and being similarly arranged with respective slots constructed similarly to the above-mentioned slot and spaced from the above-mentioned slot so as to intersect other of the tube means, said folded parts being positioned so that only a portion of the total number of tube means are intersected thereby.
 23. An arrangement according to claim 15, wherein a plurality of folded parts are provided, each of said folded parts being similar to the above-mentioned folded part and being similarly arranged with respective slots constructed similarly to the above-mentioned slot and spaced from the above-mentioned slot so as to intersect other of the tube means, said folded parts being positioned so that only a portion of the total number of tube means are intersected thereby.
 24. An arrangement according to claim 23, wherein each of said folded parts intersect a plurality of said tube means, and wherein lines interconnecting the tubes intersected by respective ones of said folded parts extend substantially parallel to one another.
 25. An arrangement according to claim 23, wherein each of said folded parts intersects a plurality of said tube means, wherein said chamber wall means is an annular shaped plate extending around a central axis of the heat exchanger arrangement, and wherein lines interconnecting the tube means intersected by respective ones of said folded parts extend radially with respect to said central axis. 